[PPT] - Characterization of Dielectric Breakdown in HighVoltage GaN MISHEMTs PowerPoint Presentation

SLIDE 1

Characterization of Dielectric Breakdown in High‐Voltage GaN MIS‐HEMTs

Shireen Warnock and Jesús A. del Alamo

Microsystems Technology Laboratories (MTL) Massachusetts Institute of Technology (MIT)

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Outline

Motivation & Challenges
Time‐Dependent Dielectric Breakdown (TDDB)

Experiments:

‒Current‐Voltage ‒Capacitance‐Voltage

Progressive Breakdown
Conclusions

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SLIDE 3

Motivation

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GaN Field‐Effect Transistors (FETs) promising for high‐voltage power applications  more efficient & smaller footprint

SLIDE 4

GaN Reliability Challenges

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Inverse piezoelectric effect

J. A. del Alamo, MR 2009

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GaN Reliability Challenges

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Inverse piezoelectric effect

J. A. del Alamo, MR 2009

Current collapse

D. Jin, IEDM 2013

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GaN Reliability Challenges

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Inverse piezoelectric effect

J. A. del Alamo, MR 2009

Current collapse

D. Jin, IEDM 2013

VT instability

SLIDE 7

GaN Reliability Challenges

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Inverse piezoelectric effect

J. A. del Alamo, MR 2009

Current collapse

D. Jin, IEDM 2013

Gate oxide reliability

VT instability

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Time‐Dependent Dielectric Breakdown

High gate bias → defect generaon → catastrophic oxide

breakdown

Often dictates lifetime of chip

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D. R. Wolters, Philips J. Res. 1985
T. Kauerauf, EDL 2005

Typical TDDB experiments: Si high‐k MOSFETs Gate material melted after breakdown

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Dielectric Reliability in GaN FETs

AlGaN/GaN metal‐insulator‐semiconductor high electron mobility transistors (MIS‐HEMTs)

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Very little currently known about TDDB in GaN  goal of this work

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TDDB Experiments: Current‐Voltage

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SLIDE 11

GaN MIS‐HEMTs for TDDB study

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P. Lagger, TED 2014

stress time ↑

GaN MIS‐HEMTs from industry

collaboration: depletion‐mode

Gate stack has multiple layers &

interfaces

→ Uncertain electric field distribution → Many trapping sites

Complex dynamics involved

→ Unstable and fast changing VT

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Classic TDDB Experiment

Constant gate voltage stress experiment:

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Experiment gives time to breakdown and shows generation of stress‐induced leakage current (SILC)

trapping SILC Hard breakdown

tBD

IG

S. Warnock, CS MANTECH 2015

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GaN TDDB Statistics

Examine statistics for different VGstress

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Weibull distribution
As VGstress ↑, tBD ↓
Parallel statistics  consistent with results in silicon

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TDDB with Periodic Characterization

Pause TDDB stress and sweep transfer characteristics at VDS=0.1 V

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Large VT shi → trapping in dielectric or AlGaN
Immediate S degradaon → interface state generation early in

experiment

VDS=0.1 V

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Validity of Characterization Approach

Compare statistics for standard and interrupted schemes

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Same stascs for both schemes → characterizaon is benign

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Step‐Stress TDDB

Step‐stress to examine early stages of degradation
Step VGstress in 0.5 V increments until breakdown

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Low VGstress: IG ↓ ⇒ trapping
High VGstress: IG ↑ ⇒ SILC

VDS=0 V

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Step‐Stress TDDB

Transfer characteristics in between stress steps

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S and VT degradation is progressive
At VGstress

12.5 V, ΔVT < 0 (red lines)

‒ Sudden increase in S, appearance of SILC→ interface state generation

VDS=0.1 V

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TDDB Experiments: Capacitance‐Voltage

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SLIDE 19

C‐V Characterization

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At VGS>1 V, conduction band of AlGaN starts being populated

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C‐V Characterization

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TDDB characterization takes place here

TDDB characterized in regime where AlGaN is populated

with electrons

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Constant VGstress TDDB

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As stress me ↑

→ CGG ↑ → Frequency dispersion ↑

Consistent with trap creation and trapping

‒ In dielectric and/or at MIS interface

CGG vs. stress time in 5 devices at 5 different frequencies:

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Progressive Breakdown

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SLIDE 23

Observation of Progressive Breakdown

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trapping SILC hard breakdown (HBD)

Revisit classic TDDB experiment: VGstress=12.6 V, VDS=0 V

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Observation of Progressive Breakdown

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Near breakdown, IG becomes noisy  progressive breakdown (PBD) Revisit classic TDDB experiment: VGstress=12.6 V, VDS=0 V

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Observation of Progressive Breakdown

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Near breakdown, IG becomes noisy  progressive breakdown (PBD) Revisit classic TDDB experiment: VGstress=12.6 V, VDS=0 V

tPBD tHBD

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PBD Statistics

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Statistics nearly parallel  breakdown mechanism is same Compare statistics for tPBD and tHBD

PBD HBD

VGstress=12.3 V VDS,stress=0 V

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PBD Statistics

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HBD, PBD uncorrelated from device to device  dielectric defect generation is truly random PBD HBD

VGstress=12.3 V VDS,stress=0 V

Examine PBD and HBD times for each individual device
PBD and HBD in same device linked by a line
S. Warnock,

IRPS 2016

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Conclusions

Developed methodology to study TDDB in GaN MIS‐

HEMTs

TDDB behavior consistent with Si MOSFETs:

‒ Weibull distribution ‒ SILC before breakdown ‒ Clear observation of Progressive Breakdown

For moderate gate voltage stress:

‒ ΔVT > 0 ‒ IG ↓

Beyond critical value of VGstress:

‒ ΔVT < 0 ‒ Sudden ΔS ↑ ‒ Capacitance frequency dispersion ↑

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SLIDE 29

Conclusions

Developed methodology to study TDDB in GaN MIS‐

HEMTs

TDDB behavior consistent with Si MOSFETs:

‒ Weibull distribution ‒ SILC before breakdown ‒ Clear observation of Progressive Breakdown

For moderate gate voltage stress:

‒ ΔVT > 0 ‒ IG ↓

Beyond critical value of VGstress:

‒ ΔVT < 0 ‒ Sudden ΔS ↑ ‒ Capacitance frequency dispersion ↑

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Consistent with electron trapping

SLIDE 30

Conclusions

Developed methodology to study TDDB in GaN MIS‐

HEMTs

TDDB behavior consistent with Si MOSFETs:

‒ Weibull distribution ‒ SILC before breakdown ‒ Clear observation of Progressive Breakdown

For moderate gate voltage stress:

‒ ΔVT > 0 ‒ IG ↓

Beyond critical value of VGstress:

‒ ΔVT < 0 ‒ Sudden ΔS ↑ ‒ Capacitance frequency dispersion ↑

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Consistent with electron trapping Onset of trap generation in dielectric/at MIS interface

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Acknowledgements

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SLIDE 32

Questions?

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